The present invention relates to a fluid powered rotary drilling assembly used for downhole drilling application with a non-rotating drill string and more specifically to such assemblies employing relatively high speed, fluid powered motors coupled with one or more stages of an epicyclic gear train. Applications for the present invention include coiled tubing oil well servicing and workover apparatus as used to drill cement out of well tubing, to deepen oil wells by drilling through well tubing and to remove mineral deposits from oil well production tubing. Other applications include open hole vertical and horizontal oil, gas, and water well drilling, highway and construction boreholes, environmental test hole drilling and blast hole quarry drilling.
There is only one type of fluid powered rotary drilling assembly for downhole drilling in general use today. This unit employs a single or multiple lobed orbiting rotor or moyno type motor which is available in several very similar variations. The orbital rotor of moyno motors in general use at this time have a rubber stator and an eccentric, orbiting rotor which have universal joints to provide axial output. These universal joints result in an undesirable increase in the length of the motor and can set up lateral vibrations and shock waves that tend to increase motor and bit wear, enlarge the borehole and may even cause caving and collapse of the borehole wall. The rubber stator is used to provide close internal clearances, while having tolerance for debris in the circulated fluid. However, these motors are not suitable for operation with compressible or semi-compressible fluids such as nitrogen foam emulsions because of high internal friction and consequent overheating and degradation of the rubber stator during such operation.
Direct drive axial turbine motors have been used in relatively small numbers. These devices operated at a relatively high rotational speed and required a larger volume of drilling fluid than would normally be used for drilling. The rotational speed was higher than desirable for drilling and the motor torque output was inadequate for drilling most formations. As a result, this type of motor is no longer used anywhere in the industry.
A first object of the present invention is therefore, to provide a fluid powered downhole drilling assembly which is capable of operation with non-compressible, semi-compressible or compressible fluids and which is capable of operation with emulsified fluids. A second object of the present invention is to provide such an assembly with a motor having a high tolerance for debris in the operating fluid. A third object of the present invention is to provide such an assembly with a motor having a high tolerance for operating at elevated down hole temperatures. A fourth object of this invention is to provide a rotationally balanced motor to minimize operational vibration of the drilling assembly. Yet other objects are to provide a downhole drilling assembly having a relatively short overall length and suitable for in line coupling to a drill bit or other well tool such as under reamers.
The present inventions satisfy the aforestated objects by providing a drilling fluid powered rotary drilling motor assembly mounted on the downhole end of a non-rotating fluid conducting drill string having a motor with a plurality of fluid engaging, rotating elements for conversion of the kinetic and pressure energies of the drilling fluid to mechanical power coupled to at least one speed reducing planetary gear stage for rotating a drill bit on the drilling assembly distal end. The drilling assembly may include a lubricator, a drilling fluid filter, a pressure relief valve, a bypass valve and a check valve and is mounted with an output isolation coupling and a bearing package sized to withstand drilling load conditions.
Pressure fluid normally circulated through the drilling system to remove borehole cuttings is supplied to a downhole motor where it acts on a plurality of fluid engaging, rotating elements to produce rotating torque forces. These forces are transmitted to a single or multiple stage planetary gear rotational speed reducing and torque increasing unit that is coupled with the motor output shaft so as to provide the lower rotational speeds needed for drilling. As a result of the high rotational input speeds allowed by the planetary gear reducer, the drilling fluid powered motors are relatively small for the horsepower produced.
The drilling fluid system of the present inventions is conditioned by the provision of a fluid filter to provide the cleanliness of the fluid for sustained motor performance. Certain fluids, such as dry gases, have no lubricating qualities, so a lubricator is provided. Also there is a wide variation of fluid pressure and volume available for power and these must be suitable for motor operation. Therefore, pressure regulator and volume bypass valves are incorporated into the present inventions.
Other important features of the present inventions are an inherently balanced rotor and gearing and an axial motor output that eliminates any need for a universal jointed driveshaft.